The microstructure evolution and its effect on the impact toughness of a new Ni-Fe based alloy GH984G, used in 700 °C ultra-super critical coal-fired power plant, were investigated during thermal exposure at 650 °C–750 °C for up to 10,000 h. The results show that the impact toughness at room temperature drops rapidly at the early stage during thermal exposure at 700 °C and then has no significant change even if after exposure for 10,000 h. The significant decline of the impact toughness is attributed to the coarsening of M₂₃C₆ carbides at grain boundaries, which weakens the grain boundary strength and leads to the aging-induced grain boundary embrittlement. The M₂₃C₆ carbides have almost no change with further thermal exposure and the impact toughness also remains stable. Additionally, the impact toughness rises with the increase of thermal exposure temperature. The size of γ′ after thermal exposure at 750 °C for 10,000 h is much bigger than that at 650 °C and 700 °C for 10,000 h. Therefore, the intragranular strength decreases significantly due to the transformation of the interaction between γ′ and dislocation from strongly coupled dislocation shearing to Orowan bowing. More plastic deformation occurs within grains after thermal exposure at 750 °C for 10,000 h, which increases the impact toughness.

在650°C–750°C的热暴露下，研究了用于700°C超超临界燃煤电厂的新型Ni-Fe基合金GH984G的组织演变及其对冲击韧性的影响。到10,000小时 结果表明，在700°C的热暴露过程中，室温下的冲击韧性在早期阶段迅速下降，即使暴露10,000 h后，其韧性也没有明显变化。冲击韧性的显着下降归因于M ₂₃ C ₆碳化物在晶界处的粗化，这削弱了晶界强度并导致了时效引起的晶界脆化。M ₂₃ C ₆进一步的热暴露，碳化物几乎没有变化，冲击韧性也保持稳定。另外，冲击韧性随着热暴露温度的升高而增加。在750°C和10,000 h下进行热暴露后，γ'的尺寸要大得多。因此，由于γ'和位错之间的相互作用从强耦合位错剪切转变为Orowan弯曲，晶粒内强度显着降低。在750°C暴露10,000 h后，晶粒内会发生更多的塑性变形，从而增加了冲击韧性。